Regeneration of hydrogen fluoride alkylation catalyst

ABSTRACT

An improved process for the regeneration of an ASO-containing HF catalyst by the removal of ASO from said catalyst through the utilization of a separation column equipped with fixed valve fractionation trays. The separation column defines a separation zone having a top zone, an intermediate zone, and a bottom zone wherein contained within the bottom zone is a series of vertically spaced, fixed valve fractionation trays, wherein each of the fixed valve fractionation trays include a plate defining a plurality of apertures and wherein fixedly spaced above each of the apertures is a valve having a shape substantially the same as the apertures for directing the flow of gas passing upwardly through the apertures of the plate into the direction substantially parallel to the plate. One important aspect of the invention includes the use of the fixed valve fractionation trays in combination with the recycling of the bottoms stream in order to minimize the amount of hydrogen fluoride that passes with the ASO of the bottoms stream of the separation column.

BACKGROUND OF THE INVENTION

This invention relates to the regeneration of a hydrogen fluoridecatalyst used in an olefin and isoparaffin alkylation process.

In the process for alkylating olefins with isoparaffins in the presenceof a hydrogen fluoride (HF) catalyst, a by-product called acid solubleoil (ASO) is produced. This ASO is soluble in the acid phase of an HFcatalyst and, because of this solubility, over time, it will build-up inthe acid phase of the HF catalyst. If not removed, a high ASOconcentration will render the HF catalyst ineffective as an alkylationcatalyst.

There are certain known methods for regenerating an HF alkylationcatalyst, which contains a concentration of ASO, by removing the ASOtherefrom. However, many of the known methods for regenerating an HFalkylation catalyst also result in a loss of HF that is lost along withthe removed ASO.

SUMMARY OF THE INVENTION

It is thus an object of this invention to provide a process forregenerating an HF alkylation catalyst containing therein aconcentration of ASO.

Another object of this invention is to provide an HF alkylation catalystregeneration process which removes ASO from such HF alkylation catalystwith a minimum of loss of HF which is removed along with the ASOproduct.

Therefore, the inventive process provides for the regeneration of an HFcatalyst used in the alkylation of olefins with isoparaffins andcontaining therein HF and ASO. Separation means for separating ASO fromthe HF catalyst is utilized. The separation means comprises a separationcolumn, which defines a separation zone with the separation zone havinga top zone, an intermediate zone, and a bottom zone, wherein containedwithin the bottom zone is a series of vertically spaced, fixed valvefractionation trays, wherein each of the fixed valve fractionation traysinclude a plate defining a plurality of appertures and wherein fixedlyspaced above each of the appertures is a valve having a shapesubstantially the same as the appertures for directing the flow of gaspassing upwardly through the appertures of the plate into the directionsubstantially parallel to the plate. HF catalyst is introduced into theintermediate zone of the separation column while a reflux of liquidisoparaffin is introduced into the top zone of the separation column anda vaporous isoparaffin stripping fluid is introduced into the bottomzone of the separation column but below the series of vertically spaced,fixed valve fractionator trays. Removed from the separation column is anoverhead stream of HF and a bottom stream of ASO.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic representation of the process which is oneembodiment of the invention;

FIG. 2 is a vertical cross-sectional view of the tray section containedin the bottom zone of the separation column;

FIG. 3 is a horizontal cross-sectional view of the bottom zone of theseparation column as viewed along section 3--3 and showing a fixed valvefractionator tray; and

FIG. 4 is a perspective view of a single representative fixed valve of afixed valve fractionator tray.

Other objects and advantages of the invention will be apparent from thedetailed description of the invention and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1 there is shown alkylation reactor 10 whichdefines an alkylation reaction zone. An olefin feed stream is introducedinto alkylation reactor 10 through conduit 12 and an isoparaffin feedstream is introduced into alkylation reactor 10 through conduit 14. Theolefin feed generally comprises one or more olefins having from 2 to 5carbon atoms, while the isoparaffin stream generally comprises isobutaneand/or isopentane. In a typical operation, the olefin feed comprises amixture of propylene and butylenes, while the isoparaffin feed comprisesprimarily isobutane. A catalyst comprising hydrogen fluoride isintroduced into alkylation reactor 10 through a conduit 16 and throughrecycle conduits 18 and 19. In a typical alkylation process operation,the HF is in the liquid phase and has a purity of at least about 90%.Fresh makeup catalyst can be introduced as required through a conduit16. The effluent from alkylation reactor 10 is passed to a settler 20 inwhich a phase separation is made between the acid phase and hydrocarbonphase. The hydrocarbon phase is removed from settler 20 through conduit22 and passes to downstream processing.

The acid phase is removed from settler 20 through conduit 24. At least aportion of the acid phase stream is recycled directly to alkylationreactor 10 through recycle conduit 19. The remainder of the acid phasestream is passed through conduit 28, having interposed therein heater 30defining a heat transfer zone and providing means for transferring heatto the acid phase stream, to separator column 32. Separator column 32defines a separation zone comprising a top zone, an intermediate zone,and a bottom zone and provides separation means for separating ASO fromthe HF of the acid phase. A purified HF stream is removed as an overheadstream from separator column 32 through conduit 18 and is recycled toalkylation reactor 10. An ASO stream can be removed as a bottoms streamfrom separator column 32 through conduits 34 and 36.

A liquid hydrocarbon reflux is introduced into the top zone of separatorcolumn 32 through conduit 38 having interposed therein condenser 40defining a heat transfer zone and providing means for transferring heatto the liquid hydrocarbon reflux. The reflux is introduced ontodistribution tray 42 located within the top zone of separator column 32.The bottom zone of separator column 32 is provided with a plurality ofvapor-liquid contacting means, such as fixed valve fractionator trays50. Stripping isobutane is directed to the bottom zone of separatorcolumn 32 by conduit 44. Interposed in conduit 44 is vaporizer 48 whichdefines a heat transfer zone and provides means for heating and/orvaporizing the stripping isobutane introduced into separator column 32.

A bottoms stream comprising ASO is removed from separator column 32through conduit 34 and passes downstream by way of conduit 36. As anadditional embodiment of the invention, at least a portion of thebottoms stream can be recycled or returned to separator column 32 by wayof conduit 52. Interposed in conduit 52 is pump 54 for providing workinput required to recycle the at least a portion of the bottoms streamto separator column 32. The at least a portion of the bottoms stream isintroduced into the intermediate zone of separator column 32 at alocation below the introduction entry point of the acid phase but abovethe bottom zone of separator column 32 wherein contained is a series ofvertically spaced, fixed valve fractionator trays 50.

FIG. 2 provides an enlarged detail of the bottom zone of separatorcolumn 32 containing the series of vertically spaced, fixed valvefractionator trays 50. Each of the vertically spaced, fixed valvefractionator trays 50 include a plate or a deck 56 having a thicknessand defining therein a pattern or plurality of appertures 60 (shown inFIG. 3) for permitting the upwardly flow of gas therethrough. Eachindividual apperture 60 defined by each plate 56 represents across-sectional area in the range of from about 0.005 square feet toabout 0.40 square feet, preferably from about 0.01 square feet to about0.30 square feet and, most preferably, from 0.015 square feet to 0.25square feet.

Provided with each fixed valve fractionator tray 50 is a downcomer 62.Each downcomer 62 can comprise vertical plates secured along oppositeedges thereof to the interior surface of separator column 32 so as toextend entirely across the interior of separator column 32. The verticalplate of downcomer 62 extends upwardly above the plane of plate 56 so asto provide an edge 64, which defines an overflow weir, having a heightof from about 0.5 inches to about 4 inches, for retaining a level ofliquid upon each plate 56. The vertical plate of downcomer 62 alsoextends downwardly to close proximity of the fixed valve fractionatortray 50 positioned below. The downcomers 62 are located on oppositesides of the interior of separator column 32 so as to guide liquids froma fixed valve fractionator tray 50 above to a fixed valve fractionatortray 50 below until the liquid passes along the last of such trays andis directed by its downcomer 62 to the bottom of separator column 32.Thus, the arrangement of fixed valve fractionator trays 50 anddowncomers 62 provide for the stairstep type flow of liquids down theinterior of separator column 32 with the liquid passing horizontallyalong each plate 56 and being directed to the tray below each downcomer62.

The liquid is held on top of each tray by gases that flow upwardlythrough separator column 32 and passing through appertures 60.Preferably, the gas flow through appertures 60 should be sufficient toprevent a substantial portion of the liquid contained on top of eachplate 56 to fall through such appertures and sufficient to maintain alevel of liquid on top of each tray 50.

Provided in FIG. 4 is a close-up perspective view of a single apperture60 and the associated fixed valve 68. As described earlier herein, eachplate 56 shall define a plurality of appertures 60, but associated witheach of such apperture 60 is a fixed valve 68 fixedly spaced above eachapperture 60. The fixed valve 68 has substantially the same shape as itsassociated apperture 60 and is provided to direct the flow of the gaseswhich are passing upwardly through appertures 60 in the horizontaldirection parallel to plate 56. This configuration provides for theintimate contacting of the upwardly flowing gases with the liquidflowing across each plate 56. The distance of the fixed space above eachapperture 60, as measured by the distance from the horizontal planeplate 56 and the horizontal plane of fixed valve 68, is in the range offrom about 0.1 inches to about 0.5 inches, preferably from about 0.15inches to about 0.45 inches and, most preferably, from 0.2 inches to 0.4inches.

The key to the success of the process in the regeneration of an HFcatalyst that contains a concentration of ASO is the use of separatorcolumn 32 that is properly equipped with fixed fractionator trays 50 asdescribed herein. It has been found that the use of such trays incombination with the other features of the inventive process provide fora separation of ASO from the ASO-containing HF catalyst with a reductionin the amount of HF that is lost along with the ASO removed from theASO-containing HF catalyst.

The ASO-containing HF catalyst is charged to the intermediate zone ofseparator column 32 at a temperature in the range of from about 200° F.to about 300° F., preferably, however, in the range of from 250° F. to295° F. The temperature of the overhead stream of purified HF comprisingHF can be in the range of from about 200° F. to about 300° F. and,preferably between 250° F. and 295° F.

As for the isoparaffin reflux stream, its temperature can be in therange of from about 40° F. to about 140° F., preferably, 60° F. to 120°F. The preferred isoparaffin for use as the isoparaffin reflux stream isisobutane.

The stripping isoparaffin stream is introduced into the bottom zone ofseparator column 32 at an entry point below the series of verticallyspaced, fixed valve fractionator trays contained within the bottom zoneof separator column 32, and is in the form of a vapor or a gas. Thisvaporous isoparaffin rises upwardly through appertures 60 of each fixedvalve fractionator tray 50 and provides for the separation of ASO and HFfrom the ASO-containing HF catalyst. The preferred stripping isoparaffinis isobutane, and it can have a temperature exceeding about 275° F. and,preferably, can be in the range of from 300° F. to 400° F.

The pressure at which column 32 is operated can generally be in therange of from 100 psia to 200 psia, preferably, from 125 psia to 175psia.

The ASO-containing HF catalyst will generally have a concentration ofASO exceeding about 1.0 weight percent ASO based on the total weight ofthe ASO-containing HF catalyst. Specifically, the ASO concentration canbe in the range of from about 1.25 weight percent to about 10 weightpercent, and, more specifically, it can be in the range of from 1.5weight percent to 5 weight percent.

The overhead stream of purified HF comprising HF shall have aconcentration of ASO that is lower than that of the ASO-containing HFcatalyst. Therefore, the ASO concentration will generally be less than1.0 weight percent.

As for the bottoms stream of ASO, it is desirable to minimize the amountof ASO in such streams; and, indeed, this is an advantage of the instantinvention in that the amount of ASO that is lost along with the ASObottoms stream is much less than for other methods of regeneration ofASO-containing HF catalyst streams. The bottoms stream will comprise ASOat a concentration of at least about 50 weight percent based on thetotal weight of the bottoms streams. Preferably, the ASO concentrationcan be at least about 60 weight percent and, more preferably, it can beat least 70 weight percent.

It is most desirable to minimize the concentration of HF in the bottomsstream in order to also minimize the amount of HF lost with the bottomsstream, thus, the HF concentration can be less than about 50 weightpercent of the bottoms stream, preferably less than about 40 weightpercent and, most preferably less than 30 weight percent.

The following example is provided to further illustrate the inventionand the benefits thereof.

EXAMPLE

The example summarizes the results of an actual installation andoperation of the invention at the Phillips Petroleum Company refinerylocated at Sweeny, Tex. The process had experienced high acid losseswith its use of a separation column containing therein conventionalsloping or inclined trays. The inclined trays were removed from theseparation column and replaced with fixed valve fractionator trays.After a period of operation, the data clearly establishes the enormouslyimproved performance of the separation column and the significantreduction in the loss of HF with the ASO bottoms product.

The following Table I provides actual HF losses for each of six timeperiods immediately prior to the modification of the separation columnand for each of seven time periods subsequent to the modification of theseparation column. The data show that the average HF lost in the ASObottoms product for the conventional process was 34,676 pounds per timeperiod and was significantly higher than the average HF loss of 18,633pounds per time period after the installation and operation of the novelprocess. These figures amounted to an average acid consumption in theassociated alkylation process of 0.12 pounds HF per barrel alkylateproduced for the conventional process versus 0.06 pounds of HF perbarrel alkylate produced for the novel process.

                  TABLE I                                                         ______________________________________                                                  LBS HF Lost With                                                                             LBS Per Bbl Alkylate                                 Time Period                                                                             ASO Product    Produced                                             ______________________________________                                        Old Process                                                                   1         42,420         0.15                                                 2         50,500         0.16                                                 3         26.260         0.09                                                 4         30,300         0.12                                                 5         26,260         0.08                                                 6         32,320         0.10                                                 Average   34,676         0.12                                                 New Process                                                                   1         17,409         0.08                                                 2         16,796         0.05                                                 3         26,521         0.07                                                 4         21,520         0.06                                                 5         22,658         0.07                                                 6         16,705         0.05                                                 7         18,633         0.06                                                           18,633         0.06                                                 ______________________________________                                    

While this invention has been described in terms of the presentlypreferred embodiment, reasonable variations and modifications arepossible by those skilled in the art. Such variations and modificationsare within the scope of the described invention and the appended claims.

That which is claimed is:
 1. A process for regenerating an HF catalyst,containing HF and Acid Soluble Oil (hereinafter "ASO"), used in anolefin and isoparaffin alkylation process, comprising:utilizingseparation means for separating ASO from said HF catalyst, saidseparation means comprises a separator column which defines a separationzone and having a top zone, an intermediate zone, and a bottom zone,wherein contained within said bottom zone are a series of verticallyspaced, fixed valve fractionation trays, wherein each of said fixedvalve fractionation trays include a plate defining a plurality ofappertures and wherein fixedly spaced above each of said appertures is avalve having a shape substantially the same as said appertures fordirecting the flow of gas passing upwardly through said appertures ofsaid plate into the direction substantially parallel to said plate;introducing said HF catalyst into said intermediate zone; introducing,as a reflux, liquid isoparaffin into said top zone; introducing intosaid bottom zone and below said series of vertically spaced, fixed valvefractionation trays a vaporous isoparaffin stripping fluid; removingfrom said top zone an overhead stream of purified HF, comprising HF;removing from said bottom zone a bottoms stream comprising ASO; andintroducing at least a portion of said bottoms stream into saidintermediate zone below the point of introduction of said HF catalyst.2. A process as recited in claim 1 wherein each of said plurality ofappertures defined by said plate represents a cross-sectional area inthe range of from about 0.005 square feet to about 0.40 square feet. 3.A process as recited in claim 2 wherein the distance of the fixed spaceabove each of said plurality of appertures as measured by the distancefrom the horizontal plane of said plate and the horizontal plane of saidvalve is in the range of from about 0.1 inches to about 0.5 inches.
 4. Aprocess as recited in claim 3 wherein the concentration of ASO in saidHF catalyst exceeds about 1.0 weight percent based on the total weightof said HF catalyst and the concentration of ASO in said overhead streamof purified HF is less than 1.0 weight percent of said overhead stream.5. A process as recited in claim 4 wherein the concentration of ASO insaid bottoms stream is at least about 50 weight percent based on thetotal weight of said bottoms stream and the concentration of HF in saidbottoms stream is less than about 50 weight percent of the total weightof said bottoms stream.